From 65860a5cd10121ef7f8b11eab0976970d7b35dcc Mon Sep 17 00:00:00 2001
From: Xander Bil <xander@biltopia.org>
Date: Fri, 6 Dec 2024 22:01:18 +0100
Subject: add solution day06

---
 src/day06.zig | 121 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)
 create mode 100644 src/day06.zig

(limited to 'src')

diff --git a/src/day06.zig b/src/day06.zig
new file mode 100644
index 0000000..bbea665
--- /dev/null
+++ b/src/day06.zig
@@ -0,0 +1,121 @@
+const std = @import("std");
+const mecha = @import("mecha");
+const print = std.debug.print;
+
+pub fn solve(part: []u8, buffer: []u8, allocator: std.mem.Allocator) !void {
+    var lines = std.mem.splitScalar(u8, buffer, '\n');
+    var grid = std.ArrayList([]u8).init(allocator);
+    defer grid.deinit();
+    var x: i32 = 0;
+    var y: i32 = 0;
+
+    var row: usize = 0;
+    while (lines.next()) |line| : (row += 1) {
+        for (line, 0..) |element, i| {
+            if (element == '^') {
+                x = @intCast(i);
+                y = @intCast(row);
+            }
+        }
+        try grid.append(@constCast(line));
+    }
+
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(&grid, x, y, allocator);
+    } else {
+        try part2(&grid, x, y, allocator);
+    }
+}
+
+fn locations(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !std.AutoHashMap(std.meta.Tuple(&.{ i32, i32 }), void) {
+    var dirx: i32 = 0;
+    var diry: i32 = -1;
+    var x = startx;
+    var y = starty;
+    var unique = std.AutoHashMap(std.meta.Tuple(&.{ i32, i32 }), void).init(allocator);
+    errdefer unique.deinit();
+
+    while (y >= 0 and y < grid.items.len and x >= 0 and x < grid.items[@intCast(y)].len) {
+        if (grid.items[@intCast(y)][@intCast(x)] == '#') {
+            x -= dirx;
+            y -= diry;
+            const temp = dirx;
+            dirx = -diry;
+            diry = temp;
+        }
+
+        try unique.put(.{ x, y }, {});
+
+        x += dirx;
+        y += diry;
+    }
+
+    return unique;
+}
+
+fn part1(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !void {
+    var locs = try locations(grid, startx, starty, allocator);
+    defer locs.deinit();
+    print("{d}\n", .{locs.count()});
+}
+
+//----------------------------PART 2---------------------------------------------
+
+fn directionToIndex(dirx: i32, diry: i32) i32 {
+    if (dirx == 0 and diry == -1) {
+        return 0;
+    } else if (dirx == 1 and diry == 0) {
+        return 1;
+    } else if (dirx == 0 and diry == 1) {
+        return 2;
+    } else {
+        return 3;
+    }
+}
+fn part2(grid: *std.ArrayList([]u8), startx: i32, starty: i32, allocator: std.mem.Allocator) !void {
+    var locs = try locations(grid, startx, starty, allocator);
+    defer locs.deinit();
+    var total: usize = 0;
+
+    var iterator = locs.keyIterator();
+    var history = try allocator.alloc(bool, grid.items.len * grid.items[0].len * 4);
+    defer allocator.free(history);
+
+    const width: i32 = @intCast(grid.items[0].len);
+
+    while (iterator.next()) |location| {
+        grid.items[@intCast(location[1])][@intCast(location[0])] = '#';
+        var dirx: i32 = 0;
+        var diry: i32 = -1;
+        var x = startx;
+        var y = starty;
+
+        for (history) |*elem| {
+            elem.* = false;
+        }
+
+        while (y >= 0 and y < grid.items.len and x >= 0 and x < grid.items[@intCast(y)].len) {
+            const index = y * width * 4 + x * 4 + directionToIndex(dirx, diry);
+            if (history[@intCast(index)]) {
+                total += 1;
+                break;
+            }
+            if (grid.items[@intCast(y)][@intCast(x)] == '#') {
+                x -= dirx;
+                y -= diry;
+                const temp = dirx;
+                dirx = -diry;
+                diry = temp;
+            }
+
+            history[@intCast(index)] = true;
+
+            x += dirx;
+            y += diry;
+        }
+
+        grid.items[@intCast(location[1])][@intCast(location[0])] = '.';
+    }
+
+    print("{d}\n", .{total});
+}
-- 
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